The rewarding/reinforcing effects of cocaine are produced by blocking reuptake of dopamine by the dopamine transporter (DAT). The DAT gene is expressed in dopaminergic neurons of the ventral midbrain, and serves as the only currently-available marker expressed almost exclusively by these cells. We have isolated the complete human gene of fifteen exons and fourteen exons and have mapped the start of transcription for the human and mouse genes. We have screened for polymorphisms in four micro-satellites in the gene's introns and have identified sequence changes in the second, sixth, and ninth exons. The gene was mapped with other markers on the human chromosome band 5p15.3, and shown not to be linked to Tourette's Syndrome in two large kindreds. This work strengthens the genetic power to detect the role of DAT in substance abuse and other neuropsychiatric disorders. Additional work to define the sequence elements that direct expression of the DAT gene to these neurons will allow the production of transgenic mice that will serve as potential animal models for human substance abuse.